Method for evaluating muscular strength characteristics

ABSTRACT

Provided is a method for evaluating muscle strength characteristics of a limb based on a muscle group model including a first pair of antagonistic one-joint muscles, a second pair of antagonistic one-joint muscles, and a pair of antagonistic two-joint muscles, where the limb has a first rod having a proximal end supported by a first joint and a second rod supported on a free end of the first rod through a second joint. The method includes: measuring a maximum output of a free end of the second rod in at least one predetermined direction; measuring orbiting outputs of the free end of the second rod in all directions in the plane; and creating a hexagonal maximum output distribution corresponding to a contribution amount of each muscle of the muscle group model based on the maximum output in the predetermined direction and the orbiting outputs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japanese PatentApplication No. 2018-158227, filed on Aug. 27, 2018. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to a method for evaluating muscular strengthcharacteristics that evaluates muscular strength characteristics oflimbs of a human or an animal.

Description of Related Art

As a model for evaluating muscles contributing to movement in atwo-dimensional plane of a limb including two joints such as an upperlimb or a lower limb, a 3-pair of 6-muscle model in which musclesprovided in the limb are classified into a first pair of antagonisticone-joint muscles, a second pair of antagonistic one-joint muscles, anda pair of antagonistic two-joint muscles is known (for example, NonPatent Document 1: OSHIMA Tom, FUJIKAWA Tomohiko, KUMAMOTO Minayori,“Effective muscle strength evaluation for respective functions usingmuscle coordinate system including one-joint muscles and twomuscles-Simple measurement method of output distribution”, Journal ofthe Japan Society for Precision Engineering, Vol. 67, No. 6, p. 943-948(2001)). In the 3-pair of 6-muscle model, a maximum output which can beexerted at a tip of the limb is represented by a hexagonal maximumoutput distribution in which maximum outputs of each muscle are summed.

A method for evaluating muscle strength characteristics which evaluatesmuscle strength characteristics of a subject based on the 3-pair of6-muscle model is known (for example, Patent Document 1: JapaneseApplication Laid-open No. 2000-210272). In Patent Document 1, themaximum output distribution is obtained based on a predetermined outputin four directions in the two-dimensional plane (a four-pointmeasurement method). Further, in Patent Document 1, the maximum outputof each muscle is calculated based on the maximum output distribution,and the calculated maximum output of each muscle is used for musclestrength evaluation in rehabilitation treatments or sports, traininginstruction evaluation, and the like.

In the four-point measurement method described in Patent Document 1,since the hexagonal maximum output distribution is obtained based on themaximum output in the four directions, the number of points of data issmall and thus reproducibility and reliability of the obtained maximumoutput distribution are poor.

In view of above, the disclosure provides a method for evaluating musclestrength characteristics which has excellent reproducibility andreliability in an obtained maximum output distribution.

SUMMARY

According to one aspect of the disclosure, a method for evaluatingmuscle strength characteristics is provided. The muscle strengthcharacteristics of a limb are evaluated based on a muscle group modelincluding a first pair of antagonistic one-joint muscles that straddlethe first joint, a second pair of antagonistic one-joint muscles thatstraddle the second joint, and a pair of antagonistic two-joint musclesthat straddle both the first and the second joints, where the limb has afirst rod having a proximal end supported by a first joint and a secondrod supported on a free end of the first rod through a second joint. Themethod includes: measuring a maximum output of a free end of the secondrod in at least one predetermined direction in a plane defined by thefirst and the second rods; measuring orbiting outputs of the free end ofthe second rod in all directions in the plane; and creating a hexagonalmaximum output distribution corresponding to a contribution amount ofeach muscle of the muscle group model based on the maximum output in thepredetermined direction and the orbiting outputs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a 3-pair of 6-muscle model for an upperlimb.

FIG. 2 is an explanatory view of a maximum output distribution at a tipof the upper limb.

FIG. 3 is an explanatory view of a measuring device.

FIG. 4 is a block diagram of the measuring device.

FIG. 5 is a flowchart of muscle strength evaluation processing.

FIG. 6 is a flowchart of approximation processing.

FIG. 7 is a diagram showing measurement results of four maximum outputsobtained by a four-point measurement method.

FIG. 8 is a diagram showing measurement results of an orbiting output.

FIG. 9A is an explanatory diagram for explaining a method forcalculating a magnified orbiting output, and FIG. 9B is a graph showingdirection dependence of a magnification factor

FIGS. 10A-10D are explanatory diagrams for explaining processing in theapproximation processing.

FIG. 11 is a diagram showing a calculated maximum output distributionand a calculated functional effective muscle strength of each muscle.

FIG. 12 is a flowchart of linear transformation processing in musclestrength evaluation processing according to a second embodiment.

FIG. 13 is an explanatory diagram for explaining the lineartransformation processing.

FIGS. 14A-14C are explanatory views for explaining a modified example ofa method for calculating a magnified orbiting output.

DESCRIPTION OF THE EMBODIMENTS

In the following, a method for evaluating muscle strengthcharacteristics according to the disclosure will be described withreference to the drawings for two exemplary embodiments used to evaluatemuscle strength characteristics of a right upper limb of a person.

First Embodiment

A method for evaluating muscle strength characteristics is based on aknown 3-pair of 6-muscle model. The 3-pair of 6-muscle model is a modelof a muscle which contributes to an output at a tip (a carpal jointportion, a tarsal joint portion) of a limb in two-dimensional movementof a limb including two joints (a shoulder joint and an elbow joint, ahip joint and a knee joint) such as an upper limb or a lower limb.Hereinafter, the 3-pair of 6-muscle model will be described in the scopenecessary for the embodiment of the disclosure.

In the 3-pair of 6-muscle model, as shown in FIG. 1, a limb 3 such as anupper limb 2 or a lower limb of a subject 1 is modeled as a two-jointlink mechanism 6 having a first rod L₁ having a proximal end pivotallysupported (supported) on a base body L₀ by a first joint J₁ and a secondrod L₂ pivotally supported (supported) on a free end of the first rod L₁by a second joint J₂. More specifically, when the upper limb is modeled,the base body L₀ corresponds to the scapula, the first joint J₁corresponds to the shoulder joint, the first rod L₁ corresponds to thehumerus, the second joint J₂ corresponds to the elbow joint, and thesecond rod L₂ corresponds to at least one of the radius and the ulna.Further, a free end J₃ of the second rod L₂ corresponds to the carpaljoint portion. Hereinafter, the free end J₃ of the second rod L₂ will bereferred to as a limb tip J₃.

The 3-pair of 6-muscle model which models muscles contributing tomovement in a two-dimensional plane including the first joint J₁, thesecond joint J₂ and the limb tip J₃ of the limb 3 includes a first pairof antagonistic one-joint muscles f₁ and e₁ which straddle the firstjoint J₁, a second pair of antagonistic one-joint muscles f₂ and e₂which straddle the second joint J₂, and a pair of antagonistic two-jointmuscles f₃ and e₃ which straddle both the joints J₁ and J₂.

The first pair of antagonistic one-joint muscles f₁ and e₁ includes amuscle f₁ which bends the first joint J₁ and a muscle e₁ which stretchesthe first joint J₁. One ends of the muscles f₁ and e₁ of the first pairof antagonistic one-joint muscles are attached to the base body L₀, theother ends thereof are attached to the first rod L₁, and the muscles f₁and e₁ are provided to straddle the first joint J₁. The firstantagonistic one-joint muscle f₁ corresponds to, for example, a frontportion of the deltoid muscle, and the first antagonistic one-jointmuscle e₁ corresponds to, for example, a rear portion of the deltoidmuscle.

The second pair of antagonistic one-joint muscles f₂ and e₂ includes amuscle f₂ which bends the second joint J₂ and a muscle e₂ whichstretches the second joint J₂. One ends of the muscles f₂ and e₂ of thesecond pair of antagonistic one-joint muscles are attached to the firstrod L₁, the other ends thereof are attached to the second rod L₂, andthe muscles f₂ and e₂ are provided to straddle the second joint J₂. Thesecond antagonistic one-joint muscle f₂ corresponds to, for example, thebrachial muscle, and the second antagonistic one-joint muscle e₂corresponds to, for example, an outer head of the triceps brachiimuscle.

The pair of antagonistic two-joint muscles f₃ and e₃ includes a musclef₃ which simultaneously bends the first joint J₁ and the second joint J₂and a muscle e₃ which simultaneously stretches the first joint J₁ andthe second joint J₂. One ends of the pair of antagonistic two-jointmuscles f₃ and e₃ are attached to the base body L₀, the other endsthereof are attached to the second rod L₂, and the pair of antagonistictwo-joint muscles f₃ and e₃ are provided to straddle the first joint J₁and the second joint J₂. The antagonistic two muscle f₃ corresponds to,for example, the biceps brachii muscle, and the antagonistic two-jointmuscle e₃ corresponds to, for example, an elongated head of the tricepsbrachii muscle.

A magnitude and direction of the output at the limb tip J₃ aredetermined by a combination of the outputs of the first pair ofantagonistic one-joint muscles f₁ and e₁, the second pair ofantagonistic one-joint muscles f₂ and e₂, and the pair of antagonistictwo-joint muscles f₃ and e₃. Assuming that a maximum output which thefirst antagonistic one-joint muscle f₁ outputs to the limb tip J₃ isF_(f1), a maximum output which the first antagonistic one-joint musclee₁ outputs to the limb tip J₃ is F_(e1), a maximum output which thesecond antagonistic one-joint muscle f₂ outputs to the limb tip J₃ isF_(f2), a maximum output which the second antagonistic one-joint musclee₂ outputs to the limb tip J₃ is F_(e2), a maximum output which theantagonistic two-joint muscle f₃ outputs to the limb tip J₃ is F_(f3),and a maximum output which the antagonistic two-joint muscle e₃ outputsto the limb tip J₃ is F_(e3), a distribution diagram (hereinafter,maximum output distribution) of the maximum output obtained at the limbtip J₃ by these 3 pairs of 6 muscles is simply represented by a hexagonABCDEF corresponding to the contribution of each muscle, as shown inFIG. 2. However, the maximum output (hereinafter, functional effectivemuscle strength) of each muscle is the largest force that each musclecan exert (output) and is represented by a vector in a plane defined bythe first rod L₁ and the second rod L₂. Details of a method ofcalculating the hexagon ABCDEF are not described here because they areknown, but for example, reference may be made to Non-Patent Document 1described above.

In the hexagon ABCDEF, a side AB, a side DE, and the second rod L₂ areparallel to each other, and a side CD, a side FA, and the first rod L₁are parallel to each other. Further, a side BC, a side EF, and astraight line which connects the limb tip J₃ to the first joint J₁ areparallel to each other. In FIG. 2, an output F_(A) at a point A, anoutput F_(B) at a point B, an output F_(C) at a point C, an output F_(D)at a point D, an output F_(E) at a point E, and an output F_(F) at apoint F are expressed by Equation (1). The functional effective musclestrengths F_(f1), F_(f2), F_(f3), F_(e1), F_(e2) and F_(e3) of musclescan be calculated from the hexagon ABCDEF using Equation (1).

$\begin{matrix}\left\{ \begin{matrix}{F_{A} = {F_{f\; 1} + F_{e\; 2} + F_{e\; 3}}} \\{F_{B} = {F_{e\; 1} + F_{e\; 2} + F_{e\; 3}}} \\{F_{C} = {F_{e\; 1} + F_{f\; 2} + F_{e\; 3}}} \\{F_{D} = {F_{e\; 1} + F_{f\; 2} + F_{f\; 3}}} \\{F_{E} = {F_{f\; 1} + F_{f\; 2} + F_{f\; 3}}} \\{F_{F} = {F_{f\; 1} + F_{e\; 2} + F_{f\; 3}}}\end{matrix} \right. & (1)\end{matrix}$

Next, a measuring device 10 for implementing the method for evaluatingmuscle strength characteristics according to the first embodiment willbe described with reference to FIG. 3. The measuring device 10 includesa seat, a backrest 11 coupled to a rear of the seat, and a first link 12of which one end is coupled to the backrest 11, a second link 13 coupledto the other end of the first link 12, and an arithmetic device 14(refer to FIG. 4).

The first link 12 is a bar-like member which is substantially horizontaland extends in one direction. One end side of the first link 12 in anextension direction is coupled to the backrest 11 so that the first link12 is pivotable about an axis X extending in a vertical direction. Afirst actuator 16 which changes a length of the first link 12 in theextension direction and a first control device 17 which controls drivingof the first actuator 16 are provided at the first link 12. A firstangle sensor 18 which measures a rotation angle of the first link 12with respect to the backrest 11 and a known first locking mechanism 19which locks the first link 12 so that it does not rotate with respect tothe backrest 11 are provided between the first link 12 and the backrest11.

The second link 13 is a bar-like member which is substantiallyhorizontal and extends in one direction. One end side of the second link13 in an extension direction is coupled to the other end side of thefirst link 12 in the extension direction so that the second link 13 ispivotable about an axis Y extending in the vertical direction. A secondactuator 26 which changes a length of the second link 13 in theextension direction and a second control device 27 which controlsdriving of the second actuator 26 are provided at the second link 13. Asecond angle sensor 28 which measures a rotation angle of the secondlink 13 with respect to the first link 12 and a known second lockingmechanism 29 which locks the second link 13 so that it does not rotatewith respect to the first link 12 are provided between the first link 12and the second link 13. A plurality of belts 31 (fixing tools) forfixing a forearm 30 of the subject 1 are provided on the second link 13at intervals in the extension direction thereof.

A force sensor 32 is provided on the other end side of the second link13, that is, on the free end side of the second link 13. The forcesensor 32 is a known sensor which detects an in-plane force applied toan upper surface of the force sensor and is disposed in a manner thatthe upper surface of the force sensor 32 is flush with an upper surfaceof the second link 13 and is substantially horizontal. The force sensor32 may be, for example, a capacitive sensor. In this embodiment, asshown in FIG. 3, the force sensor 32 divides a vector F of a forceapplied to the upper surface of the force sensor 32 into a component Fxof the force in an x-axis direction which is substantially parallel tothe backrest 11 and faces the right side of the subject 1 and acomponent Fy of the force in a y-axis direction which is perpendicularto the x axis and faces a front of the subject 1 and then outputs them.The vector F of the force measured by the force sensor 32 corresponds toone point (Fx, Fy) on xy coordinates defined in a substantiallyhorizontal plane with the upper surface of the force sensor 32 as anorigin O.

As shown in FIG. 4, the arithmetic device 14 is a computer including anarithmetic processing unit 35 such as a central processing unit (CPU)which performs arithmetic processing, a storage unit 36 such as a memoryand a hard disk which holds information, an output unit 37 such as adisplay 37A and a speaker 37B, and an input unit 38. The arithmeticdevice 14 is connected to the first angle sensor 18, the second anglesensor 28, the first control device 17, the second control device 27,and the force sensor 32 through a predetermined cable at the input unit38.

When the muscle strength of the upper limb 2 of the subject 1 isevaluated, after the subject 1 sits on the seat, his/her back is placedalong the backrest 11, and his/her torso is fixed to the backrest 11 bya belt or the like. Therefore, since the subject's torso does not move,the muscle strength characteristics can be evaluated more appropriately.Thereafter, the subject 1 places an upper arm 40 along the upper surfaceof the first link 12 and places the forearm 30 along the upper surfaceof the second link 13. At this time, the subject 1 drives the firstactuator 16 and the second actuator 26 so that the shoulder joint (thefirst joint) J₁ is aligned with the axis X, the elbow joint (the secondjoint) J₂ is aligned with the axis Y and the carpal joint (the limb tip)J₃ is in contact with the upper surface of the force sensor 32, and thusthe length of each of the first link 12 and the second link 13 may beadjusted. Next, the subject 1 fixes the forearm 30 to the second link 13using the belt 31 and locks the links 12 and 13 such that they do notrotate using the locking mechanisms 19 and 29. Thereafter, thearithmetic device 14 performs the muscle strength evaluation processing.

While the muscle strength evaluation processing is performed, thehumerus (the first rod) L₁, and the radius and ulna (the second rod) L₂of the subject 1 are disposed along a substantially horizontalmeasurement surface H (refer to FIG. 8). Further, the shoulder joint J₁(the first joint) of the subject 1 and the elbow joint J₂ (the secondjoint) are held at a predetermined angle by the locking of the lockingmechanisms 19 and 29 and the belt 31, and a posture of the subject 1 iskept constant. Also, before the muscle strength evaluation processing isperformed, the arithmetic device 14 may instruct the subject 1 to turnhis/her palm downward using sound generated from the speaker 37B.

In the muscle strength evaluation processing, the arithmetic device 14may receive a signal from the first angle sensor 18 at the input unit 38and may calculate an angle 61 (refer to FIG. 3) of the first joint J₁(the shoulder joint) of the subject 1 based on the received signal.Further, the arithmetic device 14 may receive a signal from the secondangle sensor 28 at the input unit 38 and may calculate an angle δ₂(refer to FIG. 3) of the second joint J₂ (the elbow joint) of thesubject 1 based on the received signal. The arithmetic device 14 mayreceive a signal from the first control device 17 at the input unit 38and may calculate a length l₁ (refer to FIG. 3) of the upper arm 40 ofthe subject 1, that is, the first rod L₁ based on the received signal.The arithmetic device 14 may receive a signal from the second controldevice 27 at the input unit 38 and may calculate a length l₂ (refer toFIG. 3) of the forearm 30 of the subject 1, that is, the second rod L₂based on the received signal.

Next, the muscle strength evaluation processing performed in thearithmetic device 14 will be described with reference to FIG. 5.

In initial Step ST1 of the muscle strength evaluation processing, thearithmetic device 14 measures the maximum output in four directions byinstructing the subject 1 to exert the maximum output in the fourdirections. The measurement of the maximum output in the four directionsmay be similar to the four-point measurement method described in PatentDocument 1. Specifically, first, the arithmetic device 14 instructs thesubject 1 to exert as much force as possible in a direction(hereinafter, a first direction) in which the second joint J₂ isstretched to the limb tip J₃ within a predetermined measurement time.The first direction is defined in a plane defined by the upper arm 40(the first rod L₁) and the forearm 30 (the second rod L₂), that is, in ameasurement plane H and is generally a forward direction with respect tothe subject 1. The instruction to the subject 1 may be performed usingdisplay on the display 37A or sound from the speaker 37B. The forceexerted by the subject 1 on the limb tip J₃ is applied to the uppersurface of the force sensor 32. The arithmetic device 14 extracts andstores a vector F₁ of the largest force applied to the upper surface ofthe force sensor 32 within the measurement time based on the output fromthe force sensor 32. Next, the subject 1 is instructed to exert a forceas much as possible in a direction in which the second joint J₂ bends atthe limb tip J₃, that is, in a direction opposite to the first directionwithin a predetermined measurement time. The arithmetic device 14extracts and stores a vector F₃ of the largest force applied to theupper surface of the force sensor 32 within the measurement time.

Next, the arithmetic device 14 calculates a second direction which isparallel to the measurement plane H and is orthogonal to that of adifference (F₁−F₃) between F₁ and F₃ and in which both the first jointJ₁ and the second joint J₂ are stretched. Furthermore, the arithmeticdevice 14 instructs the subject 1 to exert as much force as possible inthe second direction on the limb tip J₃ within a predeterminedmeasurement time. The arithmetic device 14 extracts and stores a vectorF₂ of the largest force applied to the upper surface of the force sensor32 within the measurement time based on an output from the force sensor32. Next, the arithmetic device 14 instructs the subject 1 to exert asmuch force as possible in a direction opposite to the second directionon the limb tip J₃ within a predetermined measurement time. Thearithmetic device 14 extracts and stores a vector F₄ of the largestforce applied to the upper surface of the force sensor 32 within themeasurement time based on an output from the force sensor 32, and thusStep ST1 is completed. As shown in FIG. 7, the four vectors F₁, F₂, F₃and F₄ of force respectively correspond to four points in the xycoordinates.

When Step ST1 is completed, the arithmetic device 14 performs Step ST2.In Step ST2, the arithmetic device 14 measures an orbiting output S ofthe limb tip J₃ in all directions in the measurement plane H. Morespecifically, the arithmetic device 14 instructs the subject 1 to exerta force in a circumferential direction, that is, while changing thedirection through 360 degrees, along the upper surface of the forcesensor 32, that is, within the measurement plane H from the limb tip J₃over a predetermined measurement time (for example, 5 seconds to 10seconds). In the embodiment, the arithmetic device 14 instructs thesubject 1 to exert a force while changing the direction in a clockwisedirection (a direction of an arrow in FIG. 8) in a top view. At thistime, the arithmetic device 14 does not need to instruct the subject 1to exert as much force as possible on the upper surface of the forcesensor 32. The arithmetic device 14 obtains a vector of force applied tothe upper surface of force sensor 32 at predetermined timings within themeasurement time based on the output from force sensor 32. Furthermore,the arithmetic device 14 stores a group of the vectors of force acquiredwithin the measurement time as the orbiting output S, and thus Step ST2is completed. The orbiting output S corresponds to a group of points(refer to FIG. 8) arranged approximately in the form of a ring in the xycoordinates.

When Step ST2 is completed, the arithmetic device 14 performs Step ST3.In Step ST3, the arithmetic device 14 calculates a half straight lineOF₁, a half straight line OF₂, a half straight line OF₃ and a halfstraight line OF₄ extending outward through each point with the origin Oas a starting point with respect to each point of the maximum outputsF₁, F₂, F₃ and F₄. Next, for each point of the maximum outputs F₁, F₂,F₃ and F₄, the arithmetic device 14 extracts a point closest to thecorresponding half straight line from the orbiting output S. Thereafter,the arithmetic device 14 calculates ratios α₁, α₂, α₃ and α₄ of adistance between the extracted point and the origin O to a magnitude ofthe corresponding maximum output. For example, when the point closest tothe half straight line OF₁ with respect to the maximum output F₁ is F₁′,α₁ is expressed as α₁=|F₁|/|F₁′|. Here, |x| represents a distance fromthe origin O (that is, the magnitude of the vector of force).

Next, angles θ₁, θ₂, θ₃ and θ₄ with respect to the x axis are calculatedfor the maximum outputs F₁, F₂, F₃ and F₄, respectively. For each pointF_(S) of the orbiting output S, an angle θ between the x-axis and astraight line connecting the point with the origin O is calculated, anda magnification factor k for each of vectors F_(S) of force included inthe orbiting output S is calculated based on the following Equation (2).

$\begin{matrix}\left\{ \begin{matrix}{k = {{\frac{\alpha_{1} - \alpha_{2}}{\theta_{1} - \theta_{2}} \cdot \left( {\theta - \theta_{2}} \right)} + \alpha_{2}}} & \left( {\theta_{2} \leq \theta < \theta_{1}} \right) \\{k = {{\frac{\alpha_{2} - \alpha_{3}}{\theta_{2} - \theta_{3}} \cdot \left( {\theta - \theta_{3}} \right)} + \alpha_{3}}} & \left( {\theta_{3} \leq \theta < \theta_{2}} \right) \\{k = {{\frac{\alpha_{3} - \alpha_{4}}{\theta_{3} - \theta_{4}} \cdot \left( {\theta - \theta_{4}} \right)} + \alpha_{4}}} & \left( {\theta_{4} \leq \theta < \theta_{3}} \right) \\{k = {{\frac{\alpha_{4} - \alpha_{1}}{\theta_{4} - \theta_{1}} \cdot \left( {\theta - \theta_{1}} \right)} + \alpha_{1}}} & \left( {\theta_{1} \leq \theta < \theta_{4}} \right)\end{matrix} \right. & (2)\end{matrix}$

The magnification factor k is represented by a linear function of theangle θ shown in Equation (2) in each of a region I sandwiched by thehalf straight line OF₁ and the half straight line OF₂, a region IIsandwiched by the half straight line OF₂ and the half straight line OF₃,a region III sandwiched by the half straight line OF₃ and the halfstraight line OF₄ and a region IV sandwiched by the half straight lineOF₄ and the half straight line OF₁ shown in FIG. 9A. Also, therelationship between k and θ is shown in FIG. 9B. The magnificationfactor k corresponds to that linearly interpolated for the angle θ withrespect to the x axis using the magnification factors α₁, α₂, α₃ and α₄at boundaries in the regions I, II, III and IV.

Next, the arithmetic device 14 performs magnification correction on theorbiting output S and calculates a magnified orbiting output P (refer toFIG. 9A) by multiplying each of the vectors of force included in theorbiting output S by the corresponding magnification factor k. Thearithmetic device 14 stores the calculated magnified orbiting output P,and thus Step ST3 is completed.

When Step ST3 is completed, the arithmetic device 14 performs Step ST4.In Step ST4, the arithmetic device 14 creates a hexagon corresponding tothe maximum output distribution Q from the magnified orbiting output P.More specifically, the arithmetic device 14 performs approximationprocessing which calculates an approximate straight line for six sidesforming the hexagon based on the magnified orbiting output P.Hereinafter, the details of the approximation processing will bedescribed below with reference to FIG. 6.

In initial Step ST11 of the approximation processing, first, thearithmetic device 14 calculates the angle δ₁ of the first joint J₁ (theshoulder joint) based on the output of the first angle sensor 18 andcalculates the angle δ₂ of the second joint J₂ (the elbow joint) basedon the output of the second angle sensor 28. Next, the arithmetic device14 calculates the length l₁ of the forearm 30 (the first rod L₁) basedon the output of the first control device 17 and calculates the lengthl₂ of the upper arm 40 (the second rod L₂) based on the output of thesecond control device 27. Thereafter, the arithmetic device 14calculates a theoretical inclination of the side corresponding to theapproximate straight line to be derived based on δ₁, δ₂, l₁ and l₂. Asshown in FIG. 2, the inclination of the side corresponding to theapproximate straight line to be derived may be calculated using thefacts that the side AB is parallel to the second rod L₂, the side CD isparallel to the first rod L₁, and the side BC is parallel to a straightline connecting the limb tip J₃ with the first joint J₁. In FIG. 10A, asan example, a straight line 50A having a theoretical inclinationcalculated with respect to the side AF and passing through the origin Ois illustrated.

When Step ST11 is completed, the arithmetic device 14 performs StepST12. In Step ST12, first, the arithmetic device 14 obtains a straightline 50B which is orthogonal to the straight line 50A having theinclination calculated in Step ST11 and passes through the origin O(FIG. 10(A)). Next, an intersection point is obtained by drawing avertical line from each point included in the magnified orbiting outputP to the obtained straight line 50B. Among the obtained intersectionpoints, a point located farthest from the origin O and located on theside (the side AB) corresponding to the approximate straight line to bederived is extracted as the maximum point 51 (FIG. 10B). The arithmeticdevice 14 stores the extracted maximum point 51, and thus Step ST12 iscompleted.

When Step ST12 is completed, the arithmetic device 14 performs StepST13. In Step ST13, the arithmetic device 14 calculates a first virtualline 52 which passes through the maximum point 51 and has thetheoretical inclination calculated in Step ST11, and a second virtualline 53 which is parallel to the first virtual line 52 and is located onthe side of the origin O by a predetermined value (for example, 50 N) ina direction orthogonal to the first virtual line 52 (FIG. 10C). Next,the arithmetic device 14 extracts and stores a point located between thefirst virtual line 52 and the second virtual line 53 in the magnifiedorbiting output P as point sequence R for fitting, and thus Step ST13 iscompleted.

When Step ST13 is completed, the arithmetic device 14 performs StepST14. In Step ST14, the arithmetic device 14 calculates an approximatestraight line 55 by fitting the point sequence R for fitting with astraight line (FIG. 10D), and thus the approximation processing iscompleted.

The arithmetic device 14 calculates six approximate straight lines 55 to60 by performing the approximation processing on each of the six sidesforming the hexagon. Therefore, as shown in FIG. 11, the arithmeticdevice 14 acquires a hexagonal maximum output distribution Q (Step ST4).After the maximum output distribution Q is acquired, in Step ST5, thearithmetic device 14 calculates functional effective muscle strengthsF_(f1), F_(f2), F_(f3), F_(e1), F_(e2) and F_(e3) of muscles from themaximum output distribution Q based on Equation (1). Further, thearithmetic device 14 may calculate the functional effective musclestrengths F_(f1), F_(f2), F_(f3), F_(e1), F_(e2) and F_(e3) of musclesby setting an appropriate numerical value to a ratio of the magnitudesof two antagonistic muscle strengths, for example,|F_(f1)|/(|F_(f1)|+|F_(e1)|) or the like, in addition to the hexagonABCDEF and Equation (1). Next, the arithmetic device 14 displaysmagnitudes of the calculated functional effective muscle strengths|F_(f1)|, |F_(f2)|, |F_(f3)|, |F_(e1)|, |F_(e2)| and |F_(e3)| of muscleson the display 37A, and thus the muscle strength evaluation processingis finished.

Next, effects of the method for evaluating muscle strengthcharacteristics configured as described above will be described. Thefour-point measurement method in which the functional effective musclestrength of each muscle is calculated based on the four maximum outputsF₁, F₂, F₃ and F₄ and the method for evaluating muscle strengthcharacteristics according to the embodiment of the disclosure wereperformed five times for the same subject 1, and the magnitude of thefunctional effective muscle strength of each muscle was calculated eachtime. Table 1 shows the magnitude of the functional effective musclestrength of each muscle calculated by the four-point measurement methodat each time and the standard deviation of the magnitude of thefunctional effective muscle strength of each muscle obtained by fivemeasurements. Table 2 shows the magnitude of the functional effectivemuscle strength of each muscle calculated by the method for evaluatingmuscle strength characteristics according to the embodiment of thedisclosure at each time and the standard deviation of the magnitude ofthe functional effective muscle strength of each muscle obtained by fivemeasurements.

TABLE 1 [N] first time second time third time fourth time fifth timestandard deviation e₁ 158.666 162.1456 113.7092 139.5818 174.152423.61623 e₂ 165.9481 145.3586 35.3795 124.1087 106.3884 50.03237 e₃78.2154 68.7963 132.5901 74.1489 75.5137 26.35103 f₁ 231.2595 233.1684180.7295 230.9553 250.8183 26.30155 f₂ 170.3982 136.8986 140.8396115.5387 105.0684 25.28612 f₃ 78.2154 68.7963 132.5901 74.1489 75.513726.35103

TABLE 2 [N] first time second time third time fourth time fifth timestandard deviation e₁ 134.1088 103.0438 123.2796 121.4134 137.546813.52776 e₂ 158.5452 221.3646 170.0726 133.4503 184.7406 32.62151 e₃85.2037 117.132 113.9932 78.4377 81.6816 18.69361 f₁ 257.5686 169.367172.3587 229.6782 223.3397 38.38877 f₂ 201.8842 145.9553 101.6415140.8392 150.271 35.75319 f₃ 85.2037 117.132 113.9932 78.4377 81.681618.69361

As shown in Table 1 and Table 2, the standard deviation obtained by themethod for evaluating muscle strength characteristics according to theembodiment is smaller than the standard deviation obtained by thefour-point measurement method in four muscles excluding f₁ and f₂.Moreover, when an average value of the standard deviation obtained bythe four-point measurement method was calculated based on Table 1, theaverage value was 29.65. On the other hand, when an average value of thestandard deviation obtained by the method for evaluating muscle strengthcharacteristics according to the embodiment was calculated based onTable 2, the average value was 26.28. From these facts, it can beconfirmed that variation in the measurement results obtained by themethod for evaluating muscle strength characteristics according to theembodiment can be minimized as compared to the case obtained by thefour-point measurement method. Thus, reproducibility and reliability ofthe maximum output distribution Q in the muscle strength evaluationmethod of the embodiment of the disclosure can be improved compared within the four-point measurement method by adding the orbiting output S tothe maximum outputs F₁ to F₄.

Further, in the embodiment, in Step ST1, the maximum outputs F₁ to F₄are measured in two or more four different directions, and in Step ST3,the magnification factor k dependent on the direction is set for eachpoint of the orbiting output S in accordance with the maximum outputs F₁to F₄ corresponding to the different directions. The orbiting output Sis magnified and corrected according to the magnification factor k, andthe magnified orbiting output P is calculated. That is, since theorbiting output S is magnified and deformed to approach the plurality ofmeasured maximum outputs F₁ to F₄, the obtained magnified orbitingoutput P approaches the actual maximum output distribution. Thus, thereproducibility and reliability of the maximum output distribution Qobtained based on the magnified orbiting output P can be enhanced.

In the embodiment, the functional effective muscle strengths F_(f1),F_(f2), F_(f3), F_(e1), F_(e2) and F_(e3) of the muscle group model,that is, the maximum output which is a contribution amount of eachmuscle is calculated based on the maximum output distribution Q.Therefore, a muscle group model close to the muscle strengthcharacteristics of the subject 1 can be constructed. Accordingly, forexample, it will be easier to identify the muscles to be reinforced inrehabilitation treatments. In addition, the muscle strength evaluationbased on the muscle group model of each of a plurality of athletes canbe performed by implementing the embodiment of the disclosure for theplurality of athletes. Thus, it is possible to carry out training basedon the evaluation.

Second Embodiment

Next, a method for evaluating muscle strength characteristics accordingto a second embodiment will be described. The method for evaluatingmuscle strength characteristics according to a second embodiment isperformed by a measurement device having the same configuration as thatin the first embodiment, and the muscle strength evaluation processingperformed by the measurement device is the same as that in the firstembodiment except Step ST3. Therefore, the details of Step ST3 will bedescribed below, and the other descriptions will be omitted.

In Step ST3, the arithmetic device 14 calculates α₁, α₂, α₃, and α₄ asin the first embodiment. Next, the arithmetic device 14 performspredetermined linear transformation processing on each of the vectorsF_(S) of force included in the orbiting output S, transforms them intoF_(P) and outputs a set of F_(P) as the magnified orbiting output P.Hereinafter, the linear transformation processing will be described indetail with reference to FIG. 12.

In initial Step ST21 of the linear transformation processing, thearithmetic device 14 determines to which one of the regions I to IVshown in FIG. 9 F_(S) belongs. In the following, the region to whichF_(S) belongs is described as a region r.

Next, in Step ST22, the arithmetic device 14 derives vectors F_(i) andF_(j) of force which define a boundary of the region r. Morespecifically, vectors of force which define the boundary of region I areF₁ and F₂, vectors of forces which define the boundary of region II areF₂ and F₃, vectors of forces which define the boundary of region III areF₃ and F₄, and vectors of forces which define the boundary of region IVare F₄ and F₁. After that, the arithmetic device 14 calculates thefollowing transformation matrix T using an x component (F_(ix)) and a ycomponent (F_(iy)) of the extracted vector F_(i) of force and an xcomponent (F_(ix)) and the y component (F_(jy)) of the extracted vectorF_(j) of force.

$\begin{matrix}{T = \begin{pmatrix}\frac{F_{ix}}{\left( \sqrt{F_{ix}^{2} + F_{iy}^{2}} \right)} & \frac{F_{jx}}{\left( \sqrt{F_{jx}^{2} + F_{jy}^{2}} \right)} \\\frac{F_{iy}}{\left( \sqrt{F_{ix}^{2} + F_{iy}^{2}} \right)} & \frac{F_{jy}}{\left( \sqrt{F_{jx}^{2} + F_{jy}^{2}} \right)}\end{pmatrix}} & (3)\end{matrix}$

The transformation matrix T is a matrix in which a vector of forcerepresented on a coordinate system having a unit vector e_(i) in adirection along the vector F_(i) and a unit vector e_(j) in a directionalong the vector F_(j) as basis vectors is transformed into a vector offorce on an xy coordinate system. The first column of the transformationmatrix represents e_(i) in the xy coordinate system, and the secondcolumn of the transformation matrix represents e_(j) in the xycoordinate system. On the other hand, an inverse matrix T⁻¹ of thetransformation matrix T is a matrix in which a vector of force in the xycoordinate system is transformed into a vector of force on thecoordinate system having e_(i) and e_(j) as basis vectors.

Next, in Step ST23, the arithmetic device 14 calculates the followingmagnification matrix A using the magnification factors α_(i) and α_(j)corresponding to F_(i) and F_(j).

$\begin{matrix}{A = \begin{pmatrix}\alpha_{i} & 0 \\0 & \alpha_{j}\end{pmatrix}} & (4)\end{matrix}$

Next, in Step ST24, the arithmetic device 14 transforms F_(S) into F_(P)using the following Equation (5), and thus the linear transformationprocessing is finished.

P _(p) =TAT ⁻¹ F _(S)  (5)

The vector F_(S) of force is represented by a linear combination ofe_(i) and e_(j) (refer to FIG. 13). More specifically, F_(S) isrepresented by the sum of a vector obtained by multiplying e_(i) by apredetermined coefficient c_(i) and a vector obtained by multiplyinge_(j) by a predetermined coefficient c_(j). As shown in FIG. 13, F_(P)obtained by the above transformation equation corresponds to a vectorobtained by integrating the magnification factors α_(i) and α_(j)corresponding to the coefficients. That is, F_(P) obtained by the abovetransformation equation is represented by the sum of a vector obtainedby multiplying e₁ by α_(i)c_(i) and a vector obtained by multiplyinge_(j) by α_(j)c_(j).

Although the description of the specific embodiment is finished, thedisclosure can be widely modified and implemented without being limitedto the above-described embodiment. The above-described embodiment isconfigured to include Step ST3 in which the muscle strength evaluationprocessing (the method for evaluating muscle strength characteristics)magnifies and corrects the orbiting output S to the maximum outputs F₁,F₂, F₃, and F₄ and calculates the magnified orbiting output P and StepST4 in which the hexagonal maximum output distribution Q correspondingto the contribution of each muscle of the muscle group model is createdbased on the magnified orbiting output P but is not limited to thisaspect. The muscle strength evaluation processing may include a step ofcreating a hexagonal maximum output distribution Q based on the maximumoutputs F₁, F₂, F₃, and F₄ and the orbiting output S. For example, themuscle strength evaluation processing may include a step of calculatinga hexagonal output distribution from the orbiting output S, and a stepof calculating a hexagonal maximum output distribution Q by magnifyingand correcting the calculated hexagonal output distribution based on themaximum outputs F₁, F₂, F₃, and F₄.

The arithmetic device 14 measures the maximum output in the fourdirections in Step ST1 but may measure the maximum output in at leastone direction. Further, the arithmetic device 14 may be configured tocalculate one magnification factor r which does not depend on adirection in Step ST3.

For example, in Step ST3, the arithmetic device 14 may extract a point Afarthest from the origin O from points corresponding to the maximumoutput and stores a distance L_(A) between the point A and the origin O(FIG. 14A). Next, a point B closest to an extracted point A is extractedfrom the orbiting output S, and a distance L_(B) between the point B andthe origin O is stored (FIG. 14B). Next, the arithmetic device 14 storesL_(A)/L_(B) as the magnification factor r. Thereafter, the arithmeticdevice 14 may be configured so that the magnification and correction isperformed by multiplying all the vectors of force included in theorbiting output S by the magnification factor r and thus themagnification orbiting output P is calculated (FIG. 14C). With such aconfiguration, it is possible to facilitate calculation of themagnification factor r.

In such a configuration, a magnitude of the maximum output distributionis obtained by the measurement of the maximum output, and an outline ofthe maximum output distribution is obtained by the measurement of theorbiting output. Thus, it is possible to reduce the number of times thesubject 1 has to exert the maximum output by separately obtaining themagnitude and the outline. Therefore, even when fatigue caused byrepeating the maximum output is likely to decrease the maximum outputthe subject 1 can exert, the maximum output distribution can be obtainedwith good reproducibility.

Further, in Step ST3, the arithmetic device 14 may calculate an annularapproximate curve using a Bezier curve or the like based on the orbitingoutput S and may calculate one magnification factor r so that a distancebetween a magnified approximate curve obtained by magnifying acalculated approximate curve and each point of the maximum output isminimized.

In the above-described embodiment, although the method for evaluatingmuscle strength characteristics is used to evaluate the muscle strengthcharacteristics of the upper limb 2 on the right side of the subject 1,it is not limited to the upper limb 2 on the right side of the subject 1and may be the upper limb 2 on the left side of the subject 1 or any ofa lower limb on the left or right side of the subject 1. Further, in theabove-described embodiment, the measurement surface is set to besubstantially horizontal. However, the disclosure is not limited to thisaspect. For example, the measurement surface may be set to besubstantially vertical. Furthermore, the method for evaluating musclestrength may be used to evaluate the muscle strength of animals such ashorses, cows and dogs.

<<Other Configurations>>

According to one aspect of the disclosure, a method for evaluatingmuscle strength characteristics is provided. The muscle strengthcharacteristics of a limb are evaluated based on a muscle group modelincluding a first pair of antagonistic one-joint muscles that straddlethe first joint, a second pair of antagonistic one-joint muscles thatstraddle the second joint, and a pair of antagonistic two-joint musclesthat straddle both the first and the second joints, where the limb has afirst rod having a proximal end supported by a first joint and a secondrod supported on a free end of the first rod through a second joint. Themethod includes: measuring a maximum output of a free end of the secondrod in at least one predetermined direction in a plane defined by thefirst and the second rods; measuring orbiting outputs of the free end ofthe second rod in all directions in the plane; and creating a hexagonalmaximum output distribution corresponding to a contribution amount ofeach muscle of the muscle group model based on the maximum output in thepredetermined direction and the orbiting outputs.

With such a configuration, the maximum output distribution can beobtained by magnifying the orbiting outputs based on the maximum output,and it is also possible to improve reproducibility and reliability ofthe maximum output distribution by combining the maximum output and theorbiting output.

In the above-described aspect, the method may further includecalculating the contribution amount of each muscle of the muscle groupmodel from the maximum output distribution.

With such a configuration, since the contribution amount of each muscleof the muscle group model is calculated, it is possible to construct amuscle group model close to the actual muscle strength characteristicsof a subject. Therefore, since it is possible to identify a muscle to bereinforced, it can be used for muscle strength evaluation inrehabilitation treatments or sports.

In the above-described aspect, measuring the maximum output andmeasuring of the orbiting outputs may be performed in a state that thefirst joint and the second joint are respectively held at predeterminedangles.

With such a configuration, since the angle of the first joint and theangle of the second joint are held when the maximum output and theorbiting output are measured, a subject's posture hardly changes, andthe reproducibility and reliability of the maximum output distributioncan be further improved.

In the above-described aspect, measuring the maximum output may beperformed in each of two or more different directions, and the orbitingoutputs may be magnified and corrected to the maximum outputcorresponding to the different directions in creating the hexagonalmaximum output distribution based on the maximum output and the orbitingoutputs.

With such a configuration, since a magnification factor depending ondirection of the orbiting output can be set based on a plurality ofmaximum outputs, the magnified orbiting output can be made closer to aplurality of measured maximum outputs. Therefore, the magnified orbitingoutput can be made closer to the actual maximum output distribution, andthe reproducibility and reliability of the maximum output distributionobtained by measurement can be enhanced.

According to the above configuration, it is possible to provide a methodfor evaluating muscle strength characteristics which has excellentreproducibility and reliability of an obtained maximum outputdistribution.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodimentswithout departing from the scope or spirit of the disclosure. In view ofthe foregoing, it is intended that the disclosure covers modificationsand variations provided that they fall within the scope of the followingclaims and their equivalents.

What is claimed is:
 1. A method for evaluating muscle strengthcharacteristics, in which the muscle strength characteristics of a limbbased on a muscle group model including a first pair of antagonisticone-joint muscles that straddle the first joint, a second pair ofantagonistic one-joint muscles that straddle the second joint, and apair of antagonistic two muscles that straddle the first and the secondjoints, where the limb has a first rod having a proximal end supportedby a first joint and a second rod supported on a free end of the firstrod through a second joint, the method comprising: measuring a maximumoutput of a free end of the second rod in at least one predetermineddirection in a plane defined by the first and the second rods; measuringorbiting outputs of the free end of the second rod in all directions inthe plane; and creating a hexagonal maximum output distributioncorresponding to a contribution amount of each muscle of the musclegroup model based on the maximum output in the predetermined directionand the orbiting outputs.
 2. The method according to claim 1, furthercomprising calculating the contribution amount of each muscle of themuscle group model from the maximum output distribution.
 3. The methodaccording to claim 1, wherein measuring the maximum output and measuringthe orbiting outputs are performed in a state that the first joint andthe second joint are respectively held at predetermined angles.
 4. Themethod according to claim 2, wherein measuring the maximum output andmeasuring the orbiting outputs are performed in a state that the firstjoint and the second joint are respectively held at predeterminedangles.
 5. The method according to claim 1, wherein measuring themaximum output is performed in each of two or more different directions,and the orbiting outputs are magnified and corrected to the maximumoutputs corresponding to different directions in creating the hexagonalmaximum output distribution based on the maximum output and the orbitingoutputs.
 6. The method according to claim 2, wherein measuring themaximum output is performed in each of two or more different directions,and the orbiting outputs are magnified and corrected to the maximumoutputs corresponding to different directions in creating the hexagonalmaximum output distribution based on the maximum output and the orbitingoutputs.
 7. The method according to claim 3, wherein measuring themaximum output is performed in each of two or more different directions,and the orbiting outputs are magnified and corrected to the maximumoutputs corresponding to different directions in creating the hexagonalmaximum output distribution based on the maximum output and the orbitingoutputs.
 8. The method according to claim 4, wherein measuring themaximum output is performed in each of two or more different directions,and the orbiting outputs are magnified and corrected to the maximumoutputs corresponding to different directions in creating the hexagonalmaximum output distribution based on the maximum output and the orbitingoutputs.